I don't know if that's true, the hordes don't venture down there just because most people when unsure just follow the herd but the tunnels are labelled in the lift and sometime in the past (about 10 years ago) HAL did the work to install travelators in there and more signage. They'd probably be happier if more people used the tunnels to take the pressure off the train.

When T5 first opened there were no travelators in the tunnels and no pictures on the walls, I think the lifts used to say 'staff only' for those levels too, although the public were never actually banned from the tunnels and I'd been using them from the start.